Process To Mold A Plastic Optical Article With Integrated Hard Coating

ABSTRACT

Disclosed is a process for molding plastic optical articles with a hard coated film, comprising steps of coating one side of an optical film with a hard coating, pre-curing the hard coating to a tack free state while still maintaining the coating flexibility, making an insert from the coated film for the desired optical article, molding the plastic resin onto the insert through insert injection molding, and post-curing the molded article. The utilization of the pre-curing and post-curing steps have been found to eliminate hard coating cracks during the insert making and the molding step, while providing a hard coating with desired properties. Such an optical article possesses a hard coating integrated on its surface, thus, eliminating the need to further coat the optical article.

RELATED APPLICATIONS

This application claims priority to provisional application Ser. No.60/401,911 filed Aug. 7, 2002, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a process for molding a plastic opticalarticle having a curved surface with integrated hard coating. The hardcoating prevents the optical article from surface scratching andabrasion. The present invention specifically relates to a process tomold a plastic optical lens, and more specifically an ophthalmic lens,with integrated hard coating through insert injection molding. Stillmore specifically, the present invention relates to a process to mold anophthalmic lens with a hard coated optical film as the insert.

DESCRIPTION OF RELATED ARTS

Optical articles such as ophthalmic lenses made from non-glassmaterials, such as polycarbonate and CR-39®, have become popular due totheir low cost and light weight. Polycarbonate provides furtheradvantages such as high refractive index and high impact resistancecompared to CR-39®. However, polycarbonate is very susceptible tosurface scratches and has low resistance to some common chemicals andsolvents compared to other materials. Application of a protective hardcoating on the surface of a non-glass ophthalmic lens is necessary forits practical use.

As a common practice, plastic optical articles such as ophthalmic lensesare hard coated after they are made, through a process such as dipcoating and spin coating. In a dip coating process, an optical articleis dipped into a coating bath filled with a coating solution and thenlifted at a given speed to yield a given coating thickness. A dipcoating process usually comprises the steps of washing the opticalarticle, drying it, dipping and lifting the article into the coatingsolution to coat it, drying the coating, and finally curing the coating.In a spin coating process, a coating solution is spin applied onto thesurface of an optical article. A typical spin coating process is similarto a dip coating process, in that the dipping step replaced by the spinstep.

Alternatively, a plastic optical article can be coated through a processknown as in-mold coating. This technique is especially useful when thesurface to be coated is shaped in a way to make either dip coating orspin coating impossible. An example of such an optical article is asegmented multi-focal lens. U.S. Pat. Nos. 4,338,269, 4,544,572,4,800,123 and 5,049,321 described in-mold coatings and processes to coatcast ophthalmic lenses. A typical process of in-mold coating comprisessteps of applying the coating to the face of a cast mold, drying and/orsemi-curing the coating, filling the mold cavity with the optical resin,and fully curing the resin and the coating. While this method issuitable for producing cast plastic or resin optical articles with harda coated surface, it is not applicable to plastic optical articles,e.g., polycarbonate ophthalmic lenses, produced through an injectionmolding process. This is primarily due to the difficulty of coating andcleaning the mold surfaces after each molding cycle.

To in-mold coat an injection molded plastic article, the following stepsare typically involved: injecting a melt of a thermoplastic resin into acavity of a mold to form a molded article, generating (through machinecontrol) a thin gap between the article surface to be coated and thecorresponding mold surface, injecting a coating composition into thegap, adjusting the gap to commensurate with a predetermined coatingthickness, curing the coating composition to form a coated moldedarticle, and withdrawing the coated molded article from the mold. Suchprocesses and coatings have been disclosed in U.S. Pat. Nos. 4,076,788,4,331,735, 4,366,109, 4,668,460, 5,777,053, and 6,180,043, and JapanesePatent Publications A-5-301251, A-5-318527, and A-8-142119 for example.While methods of in-mold coating for injection molding plastic articlesis widely used for large articles such as automobile parts, thetechnique has limited use in molding plastic optical articles such asophthalmic lenses. This limitation is primarily due to the complexinjection molding process control, difficulty in applying a hard coatingthinner than, e.g., 10 μm, extended molding cycles, and a lack ofoptical quality hard coating.

To enhance the optical quality of hard-coated, injection molded opticalarticles and to eliminate the post coating process, insert injectionmolding with a hard-coated film as an insert to mold hard-coated opticalarticles may be used. Japanese Patent Publications A-60-195515 andA-61-032004 described such a process to make hard-coated goggle lensesand polarized optical parts.

The film is typically hard-coated with a coating based on highlycross-linked acrylates or siloxanes. The coating may either be radiation(e.g., UV) curable or thermally curable. In most cases, coatings basedon acrylates are radiation cured and coatings based on siloxanes arethermally cured. Although high degree of cross-linking provides thecoating its hardness for abrasion and scratching resistance, it alsomakes the coating rather brittle with regards to the molding process.When the film is used to mold a hard coated, plastic optical articlehaving some degree of surface curvature, e.g., a polycarbonateophthalmic lens with a 6 diopter front surface, the coating will crackduring the injection molding step because it lacks the requisiteelongation characteristics.

In order to avoid cracking of coating during the injection moldingprocess, a thermoformable coating is needed. U.S. Pat. No. 4,477,499disclose a thermoformable silicone resin coating composition comprisinga colloidal silica filled thermoset organopolysiloxane containing asilylated ultraviolet radiation screening compound and a small amount ofa Lewis acid compound. U.S. Pat. No. 4,561,950 describes a radiationcurable, post-formable coating composition comprising a siliconedicarbinol diurethane diacrylate or dimethacrylate, a polyesterdiurethane diacrylate or dimethacrylate, and other functional acrylatesor acrylic acids. U.S. Pat. No. 4,598,021 disclosed a thermoformablecoating composition containing a polycaprolactone polyol and anaminoplast derivative.

U.S. Pat. No. 4,929,506 described a thermoformable polycarbonate sheetor film coated with a hard, abrasion and chemical resistant coatingwhich is the photoreaction product of an acrylated urethane oligomer, adifunctional acrylate monomer and preferably also a monofunctionalolefinic monomer.

However, the aforementioned thermoformable coatings gain the formabilityby loosing certain degree of abrasion and scratching resistance, whichis the original purpose of these coatings. They are not hard enough toprovide plastic optical articles with the desired abrasion and scratchresistance.

It is now found by the inventor that a molded, hard-coated plasticoptical article that has excellent surface optical quality and desiredabrasion and scratching resistance can be produced by a process thatmolds the thermoplastic resin material of the optical article against anoptical film having a precured hard coating.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to provide a manufacturingprocess that, utilizes the insert injection molding method and producesa molded, hard-coated plastic optical article that has excellent surfaceoptical quality and desired abrasion and scratching resistance.

The object is accomplished by using an optical film, coated on one sideof a precured or semi-cured coating, as the insert and molding thethermoplastic resin material of the optical article against theun-coated side of the optical film to thermally fuse the thermoplasticresin and the optical film together. The result is a molded, hard-coatedoptical article.

According the invention, there is a manufacturing process is providedfor producing a molded, hard-coated plastic optical article, andcomprising:

-   -   a) applying a hard coating on one side of an optical film to a        desired thickness;    -   b) precuring the hard coating to a tack free state with        predetermined conditions;    -   c) preparing the insert by punching out and pre-forming the        optical film to the designed shape to fit with the desired        products;    -   d) placing the insert in the mold cavity of a molding machine        and injection molding the resin material against the insert with        predetermined molding conditions;    -   e) curing the hard coating completely on the molded optical        article.

By the term hard coating, it is meant the coating is both abrasionresistant and scratch resistant.

The optical film can either be a single sheet or a composite functionalplate, including but not limited to a polarizing laminate plate or aphotochromic laminate plate.

The process of the present invention can be used to mold hard-coatedoptical articles such as ophthalmic lenses and sport goggle plateswithout the need of a post-coating stage after the articles are molded.Depending on the nature of the optical film, the process can be used toproduce pre-coated optical articles with additional functions such asanti-reflection compatible hard coating, polarization, photochromicproperties, etc., introduced by the optical film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a hard coated lens in accordancewith an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a molding process in accordance withan embodiment of the present invention.

DESCRIPTION OF THE INVENTION

The hard coating applicable in the process of the present invention canbe either a thermally or UV curable hard coating, although a thermallycurable coating is preferred for its superior abrasion and scratchresistance. UV curable coatings are usually based on the acrylatechemistry, and either are solventless or contain some solvents. They arecured by UV radiation. Thermally curable coatings for ophthalmic lensesare mostly siloxane based, made from hydrolyzed tetraethoxy silane, andother functional silanes. Thermally curable coatings usually have higherabrasion resistance than UV curable coatings. However, thermally curablesiloxane coatings need longer curing time than UV curable coatings. Forexample, thermally curable coatings can be found in numerous patents,such as U.S. Pat. Nos. 4,211,823, 4,547,397, 5,357,024, 5,385,955, and6,538,092. For example, UV curable coatings 4,384,026, 4,478,876,4,491,508, 5,126,394, and 5,409,965. These patents are incorporatedherein by reference.

A preferred thermally curable hard coating may have a total solidcontent of between 10% to 50% by weight, and comprise aqueous-organicsolvent mixtures containing a mixture of hydrolysis products and partialcondensates of an epoxy functional silane and a disilane and an acidiccatalyst such as a Brönsted acid, a Lewis acid, or a carboxylic acid.The solvent of the aqueous-organic solvent mixture may be selected froma group consisting of an alcohol, an ether, a glycol, a glycol ether, anester, a ketone, a glycol ether acetate and mixtures of each. Theselected solvent should not dissolve the optical film substrate to becoated. The epoxy functional silane may be selected from a groupconsisting of 3-glycidoxypropyltrimethoxysilane,3-glycidoxypropyltriethoxysilane,3-glycidoxypropylmethyldimethoxysilane,3-glycidoxypropylmethyldiethoxysilane,3-glycidoxyethoxypropylmethyldimethoxysilane, and mixtures of forgoing.Exemplary thermally curable coatings are MP-1154, MD-1183, and MP-1193from SDC Coatings (Anaheim, Calif.).

An even more preferred hard coating composition comprises componentsthat can be cross-linked by both radiation energy and thermal energy. Ifthis kind of hard coating is used to coat the optical film, radiationenergy such as UV can be used to quickly precure the coating to a tackfree state, and the final cure will be accomplished by thermal energy.U.S. Pat. No. 6,514,574 discloses such a coating composition, whichcomprises epoxy silanes, silicate, silica, thermal catalyst, andeffective amount of cationic photoinitiator. It is incorporated hereinby reference.

In the case where it is difficult to obtain adequate coating adhesion, aprimer layer may be applied onto the surface of the optical film beforethe application of the hard coating composition. The primer layerenhances the adhesion between the film substrate and the coating layer.A polyurethane or acrylic type of primer is preferred. U.S. Pat. No.5,310,577 discloses a primer consisting of a thermosetting polyurethanein at least one organic solvent, with the polyurethane being formed froma blocked isocyanate, which requires the application of heat todisassociate the blocking agent from the polyurethane so that theisocyanate group can then react with the active hydrogen of the polyolto further polymerize and crosslink the primer coating. Anotherpolyurethane primer is described in U.S. Pat. No. 5,316,791, in whichthe primer consists of an aqueous polyurethane dispersion and is driedin air at ambient or elevated temperatures. The disclosures of the aboveU.S. patents are incorporated by reference herein.

The optical film can be made from any transparent thermoplastic resinmaterial. It is preferably selected from a group consisting of aromaticpolyesters (homopolymer, copolymer, or blending), polycarbonates,cyclo-olefin homopolymers and copolymers, polyacrylates, polysulfones,polyarylates, copolymers of styrene and acrylic esters, or blends ofthermoplastic resins such as polyester and polycarbonate. It is morepreferable that the resin material of the optical film is thermallyfusible with the resin material of the optical article so that the filmbecomes a portion of the optical article without any boundary line.Thus, if the optical article is a polycarbonate ophthalmic lens, theoptical film is preferably a polycarbonate film.

If the optical film is a composite functional plate, such as apolarizing laminate plate or a photochromic laminate plate consisting ofmulti-layers, it is preferred that at least the resin material of theside that is not going to be coated is thermally fusible with the resinmaterial of the optical article to be molded.

While the thickness of an optical film is not particularly restricted,it is typically 2 mm or less, and preferably 1 mm or less but preferablynot less than 0.025 mm.

Depending on the application of the optical article to be molded, avariety of transparent resin materials can be used for molding thearticle. In case that the optical article is an ophthalmic lens or asport goggle plate, the resin material may be selected from a groupconsisting of (meth)acrylic resins, styrene-acrylate copolymers,polycarbonate resins, cyclo-olefin homopolymers and copolymers,polyurethanes, polyarylates, polysulfones, polyamides, polyimides,cellulose acetate butyrate; and acrylonitrile-butadiene-styrene.Preferred materials are bisphenol-A polycarbonates such as Panlite® fromTeijin, Lexan® from GE Plastics, and Makrolon® from Bayer Polymers.

According to one embodiment of the present invention, the manufacturingprocess for producing a molded, hard-coated plastic optical article mayinclude:

-   -   a) applying a hard coating on one side of an optical film to a        desired thickness;    -   b) precuring the hard coating to a tack free state;    -   c) preparing the insert by punching out and pre-forming the        optical film to the designed shape to fit with the desired        products;    -   d) placing the insert in the mold cavity of a molding machine,        and injection molding the resin material against the insert with        predetermined molding conditions;    -   e) curing the hard coating completely on the molded optical        article.

In Step a), a hard coating is applied to one surface of the optical filmthrough one of the conventional methods known in the art. Theses methodsinclude, but are not limited to, contact slot die coat, non-contact slotdie coat, spray coat, flow coat, gravure/flxo coat, Meyer rod coat, dipcoat, and spin coat. The optical film is usually supplied in rolls.Thus, coating application methods that are suitable for single-side webcoating process are preferred due to economic concerns. These methodsinclude slot die coat, spray coat, gravure/flexo coat, and flow coat.

The thickness of the hard coating as applied to the optical film can beselected within a broad range to meet the predetermined purpose orobjective. It is typical for the final coating thickness to be from 2 to10 microns, and preferably to be from 4 to 6 microns. The final coatingthickness depends on many parameters. For a given coating solution, thecoating thickness varies primarily with the coating application speedand the drying speed of the coated layer.

If a primer layer is needed to enhance the adhesion between the hardcoating and the optical film substrate, it can be applied in the sameway as the hard coating composition, although the desired primer layeris much thinner than the hard coating layer. The dry film thickness ofthe primer should be from about 0.1 microns to about 1.0 micron,preferably from about 0.1 to about 0.5 microns, most preferably from 0.1to 0.25 microns.

In step b), the coated optical film is transferred into thedrying/precuring area to dry and precure the coating to a tack freestate. The precuring condition obviously will depend on the formulationof the hard coating composition, the coating thickness, the energysource, and the desired degree of precuring. Typically, the temperatureof the area may be from 90° F. to 250° F. For a thermally curablecoating, it is preferred to dry and precure it at about 140 to 200° F.for about 5 to about 60 minutes. If the hard coating composition allowsprecuring with UV radiation energy, it usually takes about 10 seconds toabout 5 minutes.

At this step, the coating can also be partially cured to achieve someabrasion resistance, yet still maintain the flexibility to go throughfurther processing.

In step c), after the precuring step, the coated optical film is cutinto a shape that fits the surface of the optical article, which needsprotection from abrasion and scratching. The cut can be made in a numberof ways, including by rolling knife cutter, reciprocal stamping cutter,straight-edge cutting knife moved translationally along a cut-line, arotary or swing die traversed along a line or by laser cutter.

The optical film cuts can be optionally formed into a shape that betterfits the surface profile of the optical article. For instance, the cutsare formed into wafers of a given diopter if the optical article is anophthalmic lens. The forming process may be optionally performedthermally with or without pressure or vacuum. It is convenient toutilize a platen having a forming surface that corresponds at leastsubstantially or precisely to, the predetermined surface profile of theoptical article to be molded. The temperature for forming will vary withthe material of the transparent resin sheets. In general, thethermoforming temperature is close to but lower than the glasstransition temperature of the film resin material. For example, asuitable forming temperature for the polycarbonate optical film will befrom about 125° C. to 150° C. Often it will be beneficial to preheat thecut, for example, in the case of polycarbonate film, to a temperaturefrom about 80° C. to 120° C. for 5 to 20 minutes. U.S. Pat. No.5,434,707 describes a pressure assisted thermoforming process. U.S. Pat.No. 5,997,139 describes a vacuum assisted thermoforming process. Theirdisclosures are incorporated herein by reference.

According to the present invention, the optical film with precured hardcoating on one surface is back-molded with the thermoplastic resin tomake the optical article at Step d). Referring to FIGS. 1 and 2, to molda hard coated optical article 10 with the optical film 18 comprising thefilm base 14 and the hard coating 16 utilizing an insert injectionmolding process, the formed optical film 26 is placed in the mold cavity28 with the coated side facing the interior wall of the mold half 30.

Once the formed optical film 26 has been placed into the mold cavity 28,the two mold halves 30 and 32 close and molten resin material 24 isinjected through the runner 20 and gate 22 into the mold cavity 28 toback-mold on the uncoated side of the optical film. The combined actionof high temperature from the molten resin and high pressure from theinjection screw conforms the optical film cut 26 to the surface of theinterior wall of the mold half, and fuses the optical film and theinjected resin material together. After the resin melt is hardened, thedesired optical article is obtained having an integrated uncured hardcoating.

According to the last step of the process of the present invention, theoptical article with a pre-cured hard coating layer is exposed to aproper energy source to fully cure the hard coating. For a thermallycurable hard coating, the article is transferred into a convection oven.The cure of the coating is completed by heat curing at temperatures inthe range of 150° F. to 400° F. for a period of from about 5 minutes to18 hours. The dew point obviously plays an important role for curing asiloxane based coating. Preferably, the dew point is between 40° F. to90° F., more preferably between 50° F. to 80° F.

An added advantage of using a thermally cured hard coating is realizedat the final curing step. For most thermoplastic resin material,especially those having strong birefringence, injection molding willintroduce significant amount of internal stress in the molded products.The temperature and duration of the final curing step thermally annealedthe product to reduce the un-desirable internal stress andbirefringence.

For optical articles, such as ophthalmic lenses, made from athermoplastic resin such as polycarbonate, it is preferred to cure thehard coating at a temperature lower than the glass transitiontemperature of the resin. For polycarbonate lenses, the proper curingtemperature is between about 200° F. and 300° F.

Plastic optical articles are thus made with a hard coating integratedthereon. The post coating process is thereby eliminated.

EXAMPLES

The process of the present invention will now be illustrated in moredetail by way of an example, which are for illustration purpose only andshould not be construed as a limitation upon the scope of the inventionin any way.

The abrasion resistance is expressed as the Bayer ratio, which shows therelative abrasion resistance of the test specimen as compared with astandard lens, which is commonly manufactured and used as a benchmark inthe ophthalmic lens industry. Higher Bayer ratios indicate greaterdegrees of abrasion resistance. The Bayer ratio is determined by makingpercent haze measurements of a test specimen that is to be measured andan uncoated standard reference lens. The haze measurements of each aremade both before and after the lenses are concurrently abraded in anoscillating sand abrader as in ASTM test method F 735-81. UncoatedCR-39® (poly[di(ethylene glycol) bis(allyl carbonate)]) lenses are usedas the uncoated standard reference lenses. The abrader is oscillated for300 cycles with 500 grams of aluminum zirconium oxide, ZF 152412 assupplied by Saint Gobain Industrial Ceramics, New Bond Street, PO Box15137, Worcester, Mass. 01615. The haze is measured using a haze-guardplus haze meter from BYK Gardner. The Bayer ratio is expressed as:

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Example 1

A 0.3 mm thick polycarbonate film (Iupilon™, manufactured by MitsubishiGas Chemical Co., Inc.) was punched into discs of 72 mm. One side of thediscs was applied with three thermally-cure polysiloxane coatings (Table1). The coating solutions have a solid level of 18% to 20% and viscosityfrom 3.5 to 4.5 cPs. Coating solution was used at 50° F. The solutionwas spin applied at the speed of 500 rpm to a resulting thickness of 3to 3.5 microns.

After precuring the coating at 180° F. for 15 minutes, the discs wereplaced in the mold cavities of an injection molding machine with thecoated side facing the mold wall maintained at 285° F. Polycarbonatemelt at 600° F. was then injected into the cavity, against the uncoatedside of the film. The polycarbonate resin was then cooled down under thehold and pack pressure of 1000 psi to form semi-finished single-visionlenses with a 6-diopter base curve. The molded lenses were then put inan oven at 265° F. for 3 hours to cure the hard coating completely.Visual inspection and Bayer testing were performed on these lenses.

No sign of cracking or crazing was observed in this batch of lenses.Bayer ratios for the lenses applied by different coating solutions arelisted in table 1.

TABLE 1 Bayer ratio After Coating solutions Post-cure Tetraethoxysilane:3- 2.3 glycidoxypropyltrimethoxysilane = 1.5:1 amino propyltriethoxy silane:3- 1.8 glycido propyl trimethoxy silane = 0.6:1 aminopropyl triethoxy silane:3- 2.2 glycido propyl trimethoxy silane = 1.2:1

1. A method of producing a molded optical article comprising: applying ahard coating to one side of an optical film; precuring the hard coating;forming the optical film to a desired shape; placing the optical film ina mold cavity and injection molding a resin material; and curing thehard coating.
 2. The method of producing a molded optical article ofclaim 1, wherein the hard coating is thermally curable.
 3. The method ofproducing a molded optical article of claim 1, wherein the hard coatingis UV curable or radiation curable.
 4. The method of producing a moldedoptical article of claim 1, wherein the hard coating is applied to theoptical film with a web coating process.
 5. The method of producing amolded optical article of claim 1, wherein the hard coating is appliedto the optical film by a spin coating process.
 6. The method ofproducing a molded optical article of claim 1, wherein the optical filmis comprised of a material thermally fusible to the resin material. 7.The method of producing a molded optical article of claim 1, wherein theresin material is selected from a group consisting of polycarbonates,(meth)acrylate resins, styrene-(meth)acrylate copolymers, polysulfones,polyarylates, cyclo-olefin copolymer resins, or cellulose esters.
 8. Themethod of claim 7, wherein the optical film is comprised of a materialselected from a group consisting of polycarbonates, (meth)acrylateresins, styrene-(meth)acrylate copolymers, polysulfones, polyarylates,cyclo-olefin copolymer resins, or cellulose esters.
 9. The method ofproducing a molded optical article of claim 1, wherein the opticalarticle is an ophthalmic lens.
 10. The method of producing a moldedoptical article of claim 1, wherein the optical article is a sportgoggle plate.
 11. The method of producing a molded optical article ofclaim 1, wherein the optical film is a functional plate.
 12. The methodof claim 11, wherein the optical film is thermally fusible to theoptical article resin material.
 13. The method of claim 12, wherein theoptical film is a polarizing plate.
 14. The method of claim 13, whereinthe optical film is a photochromic plate.
 15. An eye lens comprising: alens substrate; an optical film joined with the lens substrate; and ahard coating disposed upon the optical film, the hard coating havingbeen pre-cured prior to said optical film being joined with said lenssubstrate.
 16. An optical element formed by injection moldingcomprising: a lens substrate; an optical film disposed upon the lenssubstrate; and a hard coating disposed upon the optical film, the hardcoating having been pre-cured prior to disposing said optical film onsaid lens substrate; said hard coating being substantially free ofwrinkles and cracks.